Remote sensing for the study of ecohydrology in East African Rift lakes

This thesis investigates remote sensing as a tool for monitoring the ecohydological sustainability of alkaline-saline lakes in the East African Rift Valley, of critical importance to Lesser Flamingos (Phoenicopterus minor). In Lake Bogoria, an algorithm was developed for retrieving chlorophyll-a as an indicator of cyanobacterial biomass - the Lesser Flamingos' primary food source. Results showed a strong linear relationship between Chl-a and the top-of-atmosphere Landsat ETM+ band ratio R[subscript 835]=R[subscript 660] (R[superscript 2] = 0.801; SE = 70 µg l[superscript -1]); valid for Chl-a up to 800 µg l[superscript -1]. At Lake Natron, the sole breeding site for Lesser Flamingos in East Africa, breeding is hydrologically dependent. Landsat-derived lake surface area estimates and ground-based observations of flamingo breeding showed that breeding takes place on a receding lake level. Upper and lower limits for which breeding is feasible were de fined (700-750 km[superscript 2] and 150-180 km[superscript 2] respectively) based on the presence of islands in Landsat imagery. Extending to a regional scale, a Landsat-based optical classi fication scheme was developed for alkaline-saline lakes; the scheme was able to distinguish six classes with a classifi cation accuracy of 73% when verifi ed against in situ measurements. Classifi ed imagery showed the potential importance to flamingos of the food resources off ered by Lake Logipi. Long-term timeseries of Chl-a and other environment variables for Lake Bogoria, from satellite datasets, showed that direct rainfall and lake levels were both weakly related to Chl-a and between them accounted for 20% of the variance in Chl-a. Examination of Landsat imagery showed common features associated with cyanobacterial bloom collapse in Lake Bogoria, which suggested three plausible explanations for these events. Hence, the results of this thesis have improved understanding of the connections between ecological and hydrological processes in alkaline-saline lakes and the role these lakes play in supporting the Lesser Flamingo species.